arXiv subjects

Louis S. Bouchard

Publications and source records attributed to Louis S. Bouchard.

4 recordsLinked to original sources

arXiv2025

Exchange-Coupled Spins for Robust High-Temperature Qubits

We show that Heisenberg exchange interactions between the neighboring spins comprising an ensemble spin qubit (E-qubit) can act as an intrinsic error mitigator, increasing gate fidelity even at high temperatures. As an example, the fidelity of a π gate applied to E-qubits above 1 K was studied by tuning the ferromagnetic exchange strength to show an exchange coupled E-qubit exhibits higher fidelity than a single-spin based qubit. We also investigate the coherence properties of E-qubits and find that the coherence time of an E-qubit extends linearly with the number of spins in the ensemble. This suggests that exchange interactions effectively suppress decoherence induced by thermal noise, achieving a coherence time greater than 1 ms at 1 K with an ensemble of only seven spins. Additionally, the ferromagnetic isotropic exchange prevents fidelity loss induced by spatial field gradients/inhomogeneity in Zeeman and/or control fields. Therefore, exchange-coupled spin qubits could enable fault-tolerant quantum operations and long-coherence times at elevated temperatures (>1 K).

cond-mat.mes-hall↗

arXiv2023

Proximal quantum control of spin and spin ensemble with highly localized control field from skyrmions

Selective control of individual spin qubits is needed for scalable quantum computing based on spin states. Achieving high-fidelity in both single and two-qubit gates, essential components of universal quantum computers, necessitates highly localized control fields. These fields must be capable of addressing specific spin qubits while minimizing gate errors and cross-talk in adjacent qubits. Overcoming the challenge of generating a localized radio-frequency magnetic field, in the absence of elementary magnetic monopoles, we introduce a technique that combines divergent and convergent nanoscale magnetic skyrmions. This approach produces a precise control field that manipulates spin qubits with high fidelity. We propose the use of 2D skyrmions, which are 2D analogues of 3D hedgehog structures. The latter are emergent magnetic monopoles, but difficult to fabricate. The 2D skyrmions, on the other hand, can be fabricated using standard semiconductor foundry processes. Our comparative analysis of the density matrix evolution and gate fidelities in scenarios involving proximal skyrmions and nanomagnets indicates potential gate fidelities surpassing 99.95% for π/2-gates and 99.90% for π-gates. Notably, the skyrmion configuration generates a significantly lower field on neighboring spin qubits, i.e. 15 times smaller field on a neighboring qubit compared to nanomagnets that produces the same field at the controlled qubit, making it a more suitable candidate for scalable quantum control architectures by reducing disturbances in adjacent qubits.

cond-mat.mes-hall↗

arXiv2023

Demonstration of NV-detected $^{13}$C NMR at 4.2 T

The nitrogen-vacancy (NV) center in diamond has enabled studies of nanoscale nuclear magnetic resonance (NMR) and electron paramagnetic resonance with high sensitivity in small sample volumes. Most NV-detected NMR (NV-NMR) experiments are performed at low magnetic fields. While low fields are useful in many applications, high-field NV-NMR with fine spectral resolution, high signal sensitivity, and the capability to observe a wider range of nuclei is advantageous for surface detection, microfluidic, and condensed matter studies aimed at probing micro- and nanoscale features. However, only a handful of experiments above 1 T were reported. Herein, we report $^{13}$C NV-NMR spectroscopy at 4.2 T, where the NV Larmor frequency is 115 GHz. Using an electron-nuclear double resonance technique, we successfully detect NV-NMR of two diamond samples. The analysis of the NMR linewidth based on the dipolar broadening theory of Van Vleck shows that the observed linewidths from sample 1 are consistent with the intrinsic NMR linewidth of the sample. For sample 2 we find a narrower linewidth of 44 ppm. This work paves the way for new applications of nanoscale NV-NMR.

cond-mat.mes-hall↗

arXiv2018

Color centers in diamond as novel probes of superconductivity

Magnetic imaging using color centers in diamond through both scanning and wide-field methods offers a combination of unique capabilities for studying superconductivity, for example, enabling accurate vector magnetometry at high temperature or high pressure, with spatial resolution down to the nanometer scale. The paper briefly reviews various experimental modalities in this rapidly developing nascent field and provides an outlook towards possible future directions.

cond-mat.supr-con↗